Sir Alex Ferguson, unlike many managers, had a say in who was going to succeed him at Manchester United. Photograph: Luke Macgregor/Reuters

The sickness of following a football team demands many sacrifices – the list includes jobs, marriages, friendships and lives. As such, it is unsurprising that Sir Alex Ferguson, having retired as manager of Manchester United, can find little more to do than watch Manchester United. And why shouldn't he? If David Moyes is cowed by his presence he is in the wrong job, just as Wilf McGuinness and Frank O'Farrell were when intimidated by Sir Matt Busby, his presence used by Ferguson to inspire and advise.

Nonetheless, it is impossible to assess the club's current disarray without apportioning chunks of blame in Ferguson's direction; like many greats, his strengths also manifest as weaknesses.

Most significant is the club's takeover in 2005. Before it, Ferguson had been urgent in his opposition – one that, had it sustained, might even have prevented the banks from lending the money required for its completion. But, at the time, his position was weaker than in a generation. United were mired in a second consecutive season of misery, the BBC had cast aspersions over transfer dealings involving his son Jason (which Sir Alex strongly challenged), and he developed an entirely avoidable to-do with two club directors, John Magnier and JP McManus, who openly challenged him before selling their shares. Brilliant opportunist and decisive decision-maker, he realised his value and quickly consolidated.

Since then, hundreds of millions of pounds have left the club, the consequence a hideously underfunded playing staff – which, in typical style, Ferguson turned into one of his greatest triumphs. Unable to compete with the heaviest spenders, he compensated for a relatively weak first XI by compiling a squad of variety and depth, the achievement he extracted from it baffling many observers. But this new method required twiddling so intricate as to be operable by him alone, the sum of parts now reflecting individual values.

Of course, the technical was underpinned by the interpersonal via an enveloping presence of love, fury and wisdom. The reverence with which his players regarded him was of moving, almost disquieting intensity, such that for a successor to succeed from the outset, comparable skills were essential. Instead, a very different man was appointed, lacking not only magnetism but achievements, and in this aspect, Ferguson misjudged his influence: force of personality can work only to a point, and when you're gone, you're gone. He may have implored supporters and players to believe in David Moyes, but with him at one remove, plenty of both now trust their judgment over his.

It is hard not to view his role in the appointment with a soupçon of suspicion. Very few leaders are afforded the opportunity to leave on their own terms, fewer still able to pick their replacement – yet, somehow, Ferguson managed not only this, but purloined the entire process, to the consternation of José Mourinho. And it does not take much to imagine Mourinho breezing into Old Trafford and immediately subsuming it, nor making two European Cups in 18 attempts look like professional negligence.

Conversely, Moyes worried about his attire after being summoned to attend Ferguson's house, where he was informed of – not offered – his new status. In thrall to and grateful for an opportunity he most likely did not anticipate, it is not hard to imagine the exchange envisaged as the start of a master-disciple relationship. Moyes, though, quickly showed that his is the only opinion that counts, replacing the existing coaching staff despite advice to the contrary.

Nor was he impressed with what he was left – or, put another way, Fergie's retirement was a smart move. Though the squad contains plenty of good players playing inexcusably badly, very few are at their peak, there is no discernible midfield, and little in the way of star quality; even Wayne Rooney, though good compared with those around him, is rather less so when compared with himself.

Moyes must be grateful that he is at United at all, a demob happy Ferguson getting in one last kick by reporting a transfer request that Rooney says was never issued – unsettling the process, unsettling the squad, and determining that time be expended persuading him to stay. Similarly, Fergie had also encouraged Nani to relocate – Moyes quickly awarded him a new contract – and spent part of the transfer budget on a replacement, Wilfried Zaha, who now cannot get a game.

One of Ferguson's most famous aphorisms was about knocking Liverpool off their perch – a responsibility that Liverpool fans rejoinder resides with Graeme Souness. And though there is truth in both claims, the decline began under Kenny Dalglish: key players were allowed to age together and, partly because of budgetary constraints, replaced by players of inferior quality. Dalglish still took advantage of undemanding opposition to coax them to a valedictory title but the decay was evident long before it was effective.

Despite the similarities, the game has changed enough since then such that it would be a surprise if United endured as lengthy a barren spell – but significant blame for the prospect resides with the genius who gave the club joy beyond comprehension.

• Daniel Harris' new book, The Promised Land, on Manchester United's treble season, is available here